1. Field of the Invention
The present invention pertains to a polyamide resin composition, and more specifically, to an electroconductive polyamide resin composition having high flowability, suitable for use in molding extrusion or injection components for motor vehicles requiring flexibility, impact resistance and conductivity, for example, a fuel filter housing, a fuel line, a fuel inlet tube, a fuel tank and the like that deliver fuel to a motor vehicle engine.
2. Description of the Prior Art
In general, polyamide resins are excellent in mechanical properties (e.g., tensile strength, flexible strength and elastic modulus), heat resistance and chemical resistance, and thus can be variously applied in the fields of all industries including motor vehicles, or sports. Compositions having diverse functionalities have also been applicable to many components for motor vehicles. These days, in fuel system component materials for motors, plastics have been substituted for conventional metallic materials owing to their lightweight properties, low cost and no erosion in motors. Further, polyamide resin has excellent resistance against gasoline and is employed to most fuel system components. Although a fuel filter housing or a fuel line in fuel system components should be resistant against gasoline, since they are in contact with gasoline all the time, such components have until now been made from metallic materials. Thus, polyamide resin having excellent gasoline resistance is suitable for use in preparation of such motor parts.
However, in the case of using polyamide lacking conductivity, a property necessary for fuel system components such as a fuel filter housing and a fuel line, when gasoline is fed to the engine cylinder of motors at a very rapid rate, electrostatic charges are generated due to friction between the fuel and the walls of the fuel line, and are concentrated in any one portion. Such concentrated electrical charges at any point of time are discharged at portions closest to adjacent metals. Continuous generation of such phenomenon results in fine cracks at discharged portions, through which gasoline is leaked, thus causing the danger of fire or explosion. Therefore, such motor components should have electroconductivity, capable of dissipating the static electricity to the vehicle body.
Additionally, the motor components should not be easily broken or cracked upon jarring or collision. In particular, when continuously driven in a cold area, the motor will suffer from such low temperature. So, high impact resistance and flexibility are required for the motor components.
In this regard, U.S. Pat. Nos. 5,164,084 and 5,164,879 disclose a 8% stainless steel fiber-containing polyamide-12 resin composition, which can be applied to a fuel filter housing component with conductivity, gasoline resistance and impact resistance while retaining volume resistivity of 106 Ohm-cm or less. But its preparation cost is very high and the composition is somewhat poor in flexibility and impact resistance. In U.S. Pat. Nos. 4,655,964 and 4,702,859, a polyamide resin composition is difficult to apply to a fuel filter housing, a fuel line and a fuel inlet tube because of its low impact resistance, flexibility and moldability. Japanese Patent No. Sho 58-93756 refers to a composition for application to fuel system components of motor vehicles comprising polyamide resin, ethylene based elastic copolymer and carbon black, from which a molded article is prepared, retaining electroconductivity and impact resistance but not providing high flexibility, impact and flowability. In addition, a composition comprising polyamide resin and 8-20% by weight of metallic fiber and carbon fiber for molding fuel system parts of motor vehicles, disclosed in U.S. Pat. No. 4,569,786, has excellent electroconductivity and mechanical strength, but suffers from the disadvantages of low flexibility, impact strength and flowability. Japanese Patent No. Sho 60-26057 discloses a conductive polyamide resin composition for molding, which comprises polyamide resin, metallic fiber, glass fiber and ethylene ionomer. Such composition is advantageous in light of electroconductivity and mechanical strength, but disadvantageous in terms of impact resistance, flexibility and moldability, thus not being applicable to fuel system parts in motors. A conductive thermoplastic resin composition, disclosed in Japanese Patent Nos. Sho 61-89258 and 61-207465, has excellent electrical conductivity, but has extremely poor impact resistance, flexibility and moldability. In addition, Japanese Patent No. Sho 63-51455 discloses a conductive resin composition prepared by mixing a polyamide resin with an ethylene ionomer and carbon black, to render the composition flexible and conductive. However, as for flexibility, impact resistance and flowability, the above composition does not have sufficient qualities.
U.S. Pat. No. 4,655,964 refers to a conductive nylon composition comprising a linear nylon resin, 20-50% by weight of mineral filler (kaolin, calcium metasilicate) and 4-6% by weight of carbon black, with slight conductivity. But the nylon composition suffers from low impact resistance, flexibility and moldability. Also, in U.S. Pat. No. 4,702,859, a conductive polyamide resin composition comprising 100 parts by weight of xylenediamine and aliphatic dicarboxylic acid-derived polyamide, 5-100 parts by weight of polyamide-66 resin, 30-300 parts by weight of glass fiber, 5-40 parts by weight of carbon black and 5-40 parts by weight of graphite, is excellent in conductivity, mechanical strength, elastic modulus and heat deflection temperature, but very poor in impact resistance and flexibility. As well, preparation cost is high and thus financial loss occurs. EP 0 327 384 refers to a conductive polyacetal composition having improved flexibility and toughness, which meets electrical conductivity standards but suffers from impact resistance, flexibility and moldability insufficient for use in fuel components.
In EP 0 685 527 A1, a composition comprising polyphenylene ether-polyamide resin and 1-7 parts by weight of conductive carbon black, has somewhat satisfactory conductivity, but cannot be applied to fuel components of the motor due to low impact resistance, flexibility and moldability. A composition of EP 0 866 098, which is further developed from the composition of EP 0 685 527 A1, is good in impact resistance, but is very poor in flexibility and moldability. Japanese Patent No. Hei 11-53941 discloses a conductive polyamide resin composition prepared by mixing polyamide resin A obtained from a modified polyethylene, for impact resistance, with carbon black for conductivity, potassium titanate and BBSA, which has slightly improved conductivity, flexibility and impact resistance, but is extremely poor in moldability.
Leading to the present invention, the intensive and thorough research onto materials suitable for use in fuel system components of motors, carried out by the present inventors aiming to avoid the problems encountered in the prior arts, resulted in the finding that, when a sulfonamide based material is mixed with a dicarboxyl based material, the obtained composition can be improved in various physical properties.
Therefore, the present invention has an object of providing an electroconductive polyamide resin composition, which is advantageous in light of electroconductivity, high impact resistance, high flexibility and moldability, for use in a fuel filter housing, a fuel line, a fuel inlet tube and a fuel tank as fuel system components for motor vehicles.
It is another object of the present invention to provide a molded product for a motor vehicle component prepared from the electroconductive polyamide resin composition.